1. Field of the Invention
The present invention relates to the field of reverse osmosis purification apparatus, and more specifically, to an improved reverse osmosis membrane module.
2. Prior Art
The use of reverse osmosis purification apparatus for desalinating water is well known in the art. One type of prior art process involves evaporation of, for example, brackish water or sea water in order to remove the undesirable components therefrom. The problem with such a process is that it requires a relatively high input of energy and in addition problems due to phase change of the liquid, high temperature corrosion and scaling are also present. These factors result in a high cost of the purified water so produced. Solar distillation apparatus are also used in the art and have generally proven to be of limited feasibility in most instances due to the relatively large structures required and their associated expense.
Yet another type of prior art process involves the use of a specifically configured membrane module in which a plurality of membrane sandwiches are formed such that each sandwich touches a central mandrel. This configuration is more fully set forth in U.S. Pat. No. 3,417,870. In that patent, the module is disclosed which comprises a plurality of membrane sandwiches made of coextensive leaves of sheet-like backing material which extend radially outward from a central hollow mandrel. Each leaf is associated with a sheet of semipermeable membrane such that both are wrapped around the mandrel. Care is taken in the formation of the sandwiches such that each sheet of backing material is in contact with and extends radially outward from the central mandrel. The problem with such a configuration is that only a limited number of membrane sandwiches can be formed around the central mandrel. Thus, while such configuration may be useful for a small element, if large quantities of water have to be processed, it has been found that such configuration is not sufficiently efficient. In addition, the semipermeable membrane material is folded back upon itself such that a folded edge is created along the length of contact with the mandrel. It has been found that when such a sheet of membrane is folded, there is the possibility that the fold line will substantially weaken the membrane material enabling undesirable components of the fluid to be purified to flow across the membrane. Should such a weakening and eventual flow of the fluid across the membrane be permitted, the entire membrane module would have to be removed and either repaired or replaced.
Other prior art teachings are found in U.S. Pat. Nos. 3,397,790; 3,367,504; and 3,386,583. These devices likewise contain a number of significant shortcomings which have limited their applicability in practice.
The present invention provides a spirally wrapped reverse osmosis membrane module for separating a selected fluid component from a feed stock and which substantially overcomes all of the problems associated with the prior art modules as discussed hereinabove. In addition, the membrane module of the present invention permits a relatively straight forward manner of construction to be used substantially reducing the cost and increasing the service life of each module.